Dom cram's research page

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﻿﻿I AM A BEHAVIOURAL ECOLOGIST WITH A BROAD INTEREST IN REPRODUCTION, SOCIALITY, AND HEALTH. I AM PARTICULARLY INTERESTED IN LINKS BETWEEN REPRODUCTIVE DECISIONS AND PHYSIOLOGICAL AGEING, AND I STUDY THESE LINKS IN A RANGE OF WILD SOCIAL SPECIES.﻿﻿

Suffered from illness during the recent winter? Maybe you need stronger antioxidants!

(Assuming you are a small sub-Saharan weaver bird, and your illness was experimentally induced by a standardised immune activator and a perspiring field researcher).

The immune system has frequently been linked with oxidative damage and antioxidant protection. There's even a lovely meta-analysis from 2009, which concludes that immune responses can promote oxidative stress (although it is a noisy relationship). However, almost all studies to date have been done in captivity. I wanted to see if the relationship holds in the wild.

Blood sampling a male sparrow weaver, to learn about his oxidative status

Collecting data in the wild is messy. In the lab, animals might be the same age, live in the same conditions, have the same diet, etc. In the wild, it's a complete free-for-all, and unless you know precise life-histories of your study animals, confounding effects are a risk. I wanted to avoid this by controlling for baseline oxidative status, statistically eliminating pre-existing differences between animals. After the baselines were taken from all 52 sparrow weavers in my study, I randomly allocated each bird as immune-activated or control, and again measured the oxidative status.

A fully-wild system and complete baseline measurements were the strengths of this study. And what were the results? My findings were the complete opposite of the above meta-analysis: immune-activation had no effect on oxidative damage or antioxidant protection (#1). This could be because wild birds have a range of compensatory mechanisms not feasible in captivity, that help them avoid oxidative damage (but presumably incur a cost elsewhere).

Observe as I pipette into a sealed vial, in this not-at-all staged laboratory photo.

Interestingly, in immune-activated birds, baseline antioxidant protection was linked to the size of their immune response. Birds with stronger activities of superoxide dismutase (SOD, a key antioxidant enzyme) experienced smaller inflammatory responses (#2). The importance of baseline antioxidant defences, and SOD in particular, is frequently highlighted in laboratory systems (eg in mice), but has been largely overlooked in the wild.

This was a challenging paper to write, as finding #1 was in contrast to previous studies in captivity, while finding #2 was an extension of an established laboratory finding, into a wild system. Ultimately, both captive and wild study animals have much to tell us about life-history trade-offs and physiological ageing, and I hope both fields can borrow from ideas one another frequently!

As promised in a previous post, and to help promote idea-borrowing, I decided to send this paper to PLOS one. You can find a full, free, open-access copy here.